Hard coatings of edible, chewable or pharmaceutical compositions were until recently made of sugars such as saccharose, dextrose, fructose or glucose syrups. Following intensive campaigns for the diminishment of the incidence of caries these coatings are now increasingly made using sugarfree compositions i.e. compositions containing sorbitol, xylitol, mannitol or hydrogenated starch hydrolysates.
The process for applying the coatings to the cores generally consists of rotating the cores in a rotating installation at a desired speed and temperature, applying the coating in a liquid form, allowing a film to be formed and drying the material. Variations of this process have been developed and often the process is repeated until the coatings have the desired thickness.
The polyols sorbitol and xylitol are often used in sugarfree coating applications.
International patent application WO 81/01100 describes a hard coating process. In this process the conditions are chosen in such a way that sorbitol syrup can be used as coating fluid.
EP 0 273 856 describes a process for producing a sorbitol coated comestible. The process comprises applying to a substantially anhydrous edible core at least two coating solutions comprising sorbitol to coat the edible core. The first coating solution comprises (a) about 77 to about 81 wt % sorbitol solution containing from about 65 to about 75 wt % sorbitol, and (b) about 9.5 to about 12.5 wt % crystalline sorbitol powder together with a film-forming agent and a crystallisation retardant. The second coating solution comprises (a) from about 82 to about 92 wt % sorbitol solution comprising about 65 to about 75 wt % sorbitol, and (b) about 1.0 to about 1.5 wt % crystalline sorbitol powder together with a film-forming agent and a crystallisation retardant. The solutions have a different sorbitol content and the product is dried between the application of the two layers. The product is reported to be smooth, hard and crunchy.
The coating with sorbitol as described for example in WO 81/01100 and EP 0 273 856 is widely used due to the ease of handling of this polyol. Moreover sorbitol is relatively inexpensive. The major drawback of the use of this polyol is that the resulting coating layers do not show the same crunchiness and crispiness as the conventional sucrose-based coatings. Alternatives for the use of sorbitol are therefore awaited.
Coating with xylitol is described for example in U.S. Pat. Nos. 4,105,801; 4,127,677; and 4,146,653. Xylitol is used for its cooling effect and its well-known cariostatic properties.
U.S. Pat. No. 4,238,510 describes sugarless coated comestibles wherein the coating consists essentially of sorbitol alone or in admixture with mannitol, and/or hydrogenated starch hydrolysate. Such coatings are not comparable in hardness to the coatings obtained with normally employed sugars.
Other patents describe hard coating using other polyols such as Isomalt, maltitol and erythritol (WO 95/07625 and JP 6292511).
Also the idea of a sequential coating with first several layers of one polyol and then several layers of another polyol has been proposed (U.S. Pat. No. 5,376,389). The main advantage of such a process would be the lower price of the raw material and the reduced hygroscopicity (WO 95/07622).